Abstract Based on the mineral inclusion content, diamonds from the Argyle mine, Western Australia, derive primarily (~90%) from eclogitic sources with a minor peridotitic contribution from both harzburgitic and lherzolitic lithologies. The eclogitic inclusions cover a large compositional range and, in part, show unusually high concentrations of mantle-incompatible elements (P, Ti, Na, and K). Coherent trends in major elements (e.g., of Ti or Na versus Mg-number) suggest that the eclogitic diamond source was created by a single process, namely igneous fractionation. Calculated bulk-rock chondrite-normalized rare earth element (REE N ) patterns match a section of oceanic crust reaching from lavas and sheeted dikes to upper gabbros. Positive Eu anomalies for garnet and clinopyroxene, with calculated bulk-rock REE N patterns similar to upper (nonlayered) gabbros, are strong evidence for plagioclase accumulation, which is characteristic for the gabbroic portions of oceanic crust. Linking previously published oxygen isotope analyses of eclogitic garnet inclusions with their major element composition reveals a correlation between δ 18 O (mean of 7.2‰) and Na content, consistent with coupled 18 O and Na enrichment during low-temperature alteration of oceanic crust. The carbon isotope composition of Argyle eclogitic diamonds forms a normal distribution around a δ 13 C value of −11‰, indicative of mixing and homogenization of mantle-and crustal (organic matter)-derived carbon prior to diamond precipitation. Previously published noble gas data on Argyle diamonds support this two-component model. Inclusion-and nitrogen-in-diamond–based thermometry suggests an unusually hot origin of the eclogitic diamond suite, indicative of derivation from the lowermost 25 km (about 180–205 km depth) of the local lithospheric mantle. This is consistent with emplacement of an oceanic protolith during subduction along the Kimberley craton margin, likely during the Halls Creek orogeny (about 1.85 Ga). For Argyle eclogitic diamonds, the relationship between the rate of platelet degradation and mantle residence temperature indicates that both temperature and strain play an important role in this process. Therefore, ubiquitous platelet degradation and plastic deformation of Argyle diamonds are consistent with derivation from a high-temperature environment (softening the diamond lattice) close to the lithosphere-asthenosphere boundary (inducing strain). In combination, the Argyle data set represents a uniquely strong case for a subduction origin of an eclogitic diamond source, followed by mixing of mantle and crustal components during diamond formation. Some lherzolitic inclusions show a similarity to the eclogitic suite in incompatible element enrichments (elevated P, Na, and K). The presence of a mildly majoritic lherzolitic garnet further supports a link to eclogitic diamond formation, as very similar majoritic components were found in two eclogitic garnet inclusions. The carbon isotope composition of peridotitic diamonds shows a mode between −5 and −4‰ and a tail extending toward the eclogitic mode (−11‰). This suggests the presence of multiple generations of peridotitic diamonds, with indications for an origin linked to the eclogitic suite being restricted to diamonds of lherzolitic paragenesis.

Abstract Seasonality is encoded in palaeoproxies of secondary cave mineral deposits (speleothems) and the code is becoming cracked. The petrology of calcite stalagmites from Obir, an Alpine (1100 m altitude), perennially wet cave, was characterized by optical and electron backscatter diffraction, and their chemistry by bulk ICP-MS analysis, ion microprobe and synchrotron-based micro-X-ray fluorescence. Vadose water penetrates 70 m through Triassic limestones (with some Pb–Zn mineralization) to the chamber Säulenhalle where the stalagmites were collected. Strong seasonal ventilation in the cave leads to low PCO 2 in winter associated with falls in speleothem sulphate S and increase in δ 13 C values. All samples display autumnal event lamination defined by a narrow, optically visible zone with increases in trace element concentrations, within which synchrotron studies have resolved μm-scale enrichments of Pb and Zn. Small-scale (10 µm) lateral trace element variations reflect alternate flat faces and rough crystal edges, influenced by high Zn content. The elemental covariations are consistent with the transport of Pb, Zn, P, F, Br and I adsorbed onto organic colloids in dripwater, but the final deposition may have been from aerosols and we propose this as a new mechanism requiring further investigation. This study represents the most complete demonstration of how chemical variations are powerful expressions of seasonal cave physiology in humid temperate caves, including the contrast between summer and winter conditions, and the preservation of sub-weekly events during the autumn season.